1. Field of the Invention
The invention relates to a sheet reverse conveyance device for executing a reversing operation of a sheet which is being conveyed and an image forming apparatus having such a sheet reverse conveyance device.
2. Related Background Art
Hitherto, as a sheet handling apparatus for handling a sheet, there is an image forming apparatus for forming an image onto the sheet, a document feeder for automatically feeding a document to an image reading part which is provided for the image forming apparatus and reads the document of the image forming apparatus, a sheet processor for processing the sheet on which the image has been formed by the image forming apparatus, or the like.
As an image forming apparatus, there is a copying apparatus, a laser beam printer, a facsimile apparatus, a multifunction apparatus of them, or the like. As a sheet processor, there is a stapler for stapling the sheet, a punching device for punching a hole, a folding device for folding the sheet, or the like.
In the sheet handling apparatus, there is a case where front and back sides of the sheet have to be reversed. Generally, in many cases, the image forming apparatus as a sheet handling apparatus discharges the sheet in the state where the image forming surface formed on the sheet is set to be upward (face-up). In such a case, when a document of a plurality of pages is copied, the subsequent sheet is discharged onto the precedent sheet in the state where the image forming surface is set to face-up, so that page order is reversed. Therefore, generally, in many cases, the image forming apparatus has a sheet reverse conveyance device which enables the sheet whose image forming surface is in the face-up state to be discharged in the state where the image forming surface is set to be downward (face-down). In many cases, the image forming apparatus has the sheet reverse conveyance device in order to form images onto both sides of the sheet.
As such an image forming apparatus having the sheet reverse conveyance device, there is an image forming apparatus disclosed in Japanese Patent Application Laid-open No. H08-059046.
In the sheet reverse conveyance device disclosed in Japanese Patent Application Laid-open No. H08-059046, a pair of conveyance rollers which can touch and detach are provided in an entrance portion of a reverse conveyance path. The sheet reverse conveyance device is constructed in such a manner that while the precedent sheet is being conveyed from the reverse conveyance path by a pair of discharging rollers, when the subsequent sheet is conveyed into the entrance of the reverse conveyance path, the pair of conveyance rollers are detached so that the sheets pass each other, thereby allowing the subsequent sheet to enter the reverse conveyance path while discharging the precedent sheet from the reverse conveyance path by the pair of discharging rollers.
However, according to the sheet reverse conveyance device disclosed in Japanese Patent Application Laid-open No. H08-059046, the pair of conveyance rollers for reversing the sheet conveyed into the reverse conveyance path are driven by a driving motor which can be forwardly and reversely rotated. After the sheet is conveyed in the reverse conveyance path by a predetermined amount, the rotation of the pair of conveyance rollers is decelerated and stopped and, subsequently, the pair of conveyance rollers are rotated in the opposite direction. The driving motor is also switched from the forward rotation to the reverse rotation in order to reversely rotate the pair of conveyance rollers. A predetermined stop time is required when the rotation of the driving motor is switched from the forward rotation to the reverse rotation. Therefore, the sheet reverse conveyance device disclosed in Japanese Patent Application Laid-open No. H08-059046 has a problem that the reversing operation of the sheet cannot be promptly executed.
According to Japanese Patent Application Laid-open No. H11-236157, a reverse driving roller 69 for reversing the conveying direction of a sheet and conveying the sheet is provided on a path for reversing the sheet. A reverse driven roller 68 for moving the sheet to a position where it is sandwiched between the reverse driven roller 68 and the reverse driving roller 69 and a position where it is on standby from the reverse driving roller 69 is provided. The sheet is conveyed between a reversing roller 67 and a reverse branch claw which has been come into pressure contact therewith and is conveyed into the path for reversing the sheet. Therefore, it is difficult to convey the sheet at a high speed and certainly convey the sheet into the path for reversing the sheet.